Given that the Advanced Encryption Standard [AES] has been approved
by the U.S. government (under certain usage scenarios) for top-secret
applications [AES-NSA], and that triple DES (3DES) is not susceptible
to these same attacks, one might wonder: why even bother with DES
anymore? Under more ideal circumstances, we might simply dispense
with it, but unfortunately, this would not be so simple today. DES
has been widely deployed since its release in the 1970s, and many
systems rely on it today. Wholesale replacement of such systems
would be very costly. A more realistic approach entails gradual
replacement of these systems, and this implies a term of backward
compatibility support of indefinite duration.